The invention relates to a sealed fibre optic assembly for a fibre optic gyroscope.
Fibre optic gyroscopes for measuring rotation rates are known. Such systems use the Sagnac effect in which light traverses an optic fibre loop rotating about an axis perpendicular to its plane and the optic transit time of the light around the loop varies with the loops rotation rate. If two optical signals are sent in opposite directions around the optic fibre loop, a phase difference is generated which is proportional to the rotation rate.
The object of the present invention is to provide an improved sealed fibre optic assembly for a fibre optic gyroscope.
The invention provides a sealed fibre optic assembly for a fibre optic gyroscope which assembly comprises a fibre optic support ring carrying at least one loop of optic fibre, a sealed casing surrounding said support ring and comprising a base plate, a perimeter wall upstanding from the base plate and surrounding said support ring, a cover secured to the perimeter wall so as to close the casing on the side of the support ring remote from the base plate and electrically connecting circuitry comprising external electrical terminals and electrical connectors extending from said terminals through part of the casing in sealed engagement with the casing, to the interior of the casing, and optical circuitry coupled to said loop to direct light in opposite directions around said loop and to receive light from the loop, said optical circuitry comprising a light source, a light detector and phase detecting means, and being mounted within said sealed casing, and electrically coupled to said electrical connectors in the interior of the casing.
Preferably said optical circuitry is located on said base plate within said support ring.
Preferably said electrical connectors are formed as a unit with part of the casing remote from the cover so that electrical connection may be made between the optical circuitry and the connectors while the cover is removed.
Preferably said base plate includes a projecting region outside said perimeter wall on which external electrical terminals are provided and connected to said optical circuitry.
Preferably said base plate comprises electrically insulating material and includes buried electrical connectors extending below said perimeter wall interconnecting said optical circuitry with external electrical terminals.
Preferably said optical circuitry includes at least one phase modulator.
Preferably said optical circuitry includes polarising means for polarising light transmitted around the loop.
Preferably said optical circuitry comprises an integrated semiconductor optical device.
Preferably said optical circuitry is integrated on a single planar substrate.
Preferably said integrated semiconductor optical device includes at least one silicon waveguide.
Preferably said integrated semiconductor optical device includes a plurality of silicon rib waveguides.
Preferably said perimeter wall is cylindrical.
Preferably said cover comprises a circular plate.
Preferably said base plate comprises a circular portion on which said perimeter wall is secured in sealed contact.
Preferably the perimeter wall is metallic and the base plate has a solder ring formed over an insulating layer covering the electrical connectors, the solder ring being soldered to an edge of the perimeter wall.
Preferably the cover is metallic and is soldered to the other end of the perimeter wall.
Preferably the or each optic fibre loop is wound on a spool having a cut away portion in part of the spool adjacent the base and the base has a mating projection to engage the cut away portion and hole the spool in a required rotational position relative to the base.
Preferably the or each optic fibre loop is wound on a spool having a cut away portion of sufficient arcuate extent to allow fibres to pass from the outside of the spool through the cut away portion to the optical circuitry without unwanted stress in the fibres.